Daylight hours play role in growing onions

Are you ready to plant? Dodging the snowstorms has been a little tricky, but spring will come. When it does, we will all think that we should have put in our gardens yesterday.

One of the earliest crops to go in the ground each year is onions.

Onions belong to the allium family that comprises some 600 species, including garlic, chives, scallions, leeks and flowering alliums.

Onions are an ancient crop. The pyramid builders in Egypt and Greek and Roman troops relished onions in their diets.

Onions are a diverse crop, and 26 states, including Utah, grow onions commercially. Growers across the country use more than 100 different varieties. Many of these are not available to home gardeners, but there are still plenty of good ones on the market for them.

Onions are named and classified based on flavor, color, bulb size, shape and use. They are further classified as storage, fresh, pearl or green onions.

They are also classified by an unusual characteristic. Unlike most garden vegetables, onions have a peculiar growth factor. They are sensitive to day length. The day length, or photoperiod, along with temperature, controls the bulb formation. Short-day varieties form bulbs when the day length is 12 hours or less.

Long-day plants form the best bulbs when there are 15 or more hours of daylight — when summer days are the longest. One common complaint of home gardeners is that their onions never produce big bulbs, but this is often because they plant short-day variety sets instead of long-day variety transplants or seeds.

Because the plants are sensitive to the photoperiod, some onion varieties are unsuitable for northern climates. That is because they begin to form bulbs when the plants are too small. Short day-length varieties are generally unsuitable for growing bulb onions in all but the southern parts of the United States. Long-day and a few intermediate-day varieties are usually grown in Utah.

Growing large, tasty onions takes more than just luck. Variety selection is absolutely critical because onions are either short- or long-day varieties. Long-day onions are best for our area, as they form larger bulbs here.

Onions adapt to a wide temperature range and tolerate frost. Getting them in the ground early when air temperatures of 55-75 F prevail lets the foliage and roots develop before bulbing starts.